As published

Keyword

Abstract

Results of groundwater and seawater analyses for radioactive (3H, 222Rn, 223Ra, 224Ra, 226Ra, 228Ra) and stable (2H, 18O)
isotopes are presented together with in situ spatial mapping and time-series 222Rn measurements in seawater, direct seepage
measurements using manual and automated seepage meters, pore water investigations using different tracers and piezometric
techniques, and geoelectric surveys probing the coast. This study represents first time that such a new complex arsenal of radioactive
and non-radioactive tracer techniques and geophysical methods have been used for simultaneous submarine groundwater discharge
(SGD) investigations. Large fluctuations of SGD fluxes were observed at sites situated only a few meters apart (from 0 cm d-1 to 360
cm d-1; the unit represents cm3/cm2/day), as well as during a few hours (from 0 cm d-1 to 110 cm d-1), strongly depending on the tidal
fluctuations. The average SGD flux estimated from continuous 222Rn measurements is 17±10 cm d-1. Integrated coastal SGD flux
estimated for the Ubatuba coast using radium isotopes is about 7x103 m3 d-1 per km of the coast. The isotopic composition (δ2H and
δ18O) of submarine waters was characterised by significant variability and heavy isotope enrichment, indicating that the contribution
of groundwater in submarine waters varied from a small percentage to 20%. However, this contribution with increasing offshore
distance became negligible. Automated seepage meters and time-series measurements of 222Rn activity concentration showed a
negative correlation between the SGD rates and tidal stage. This is likely caused by sea level changes as tidal effects induce variations of hydraulic gradients. The geoelectric probing and piezometric measurements contributed to better understanding of the spatial distribution of different water masses present along the coast. The radium isotope data showed scattered distributions with offshore distance, which imply that seawater in a complex coast with many small bays and islands was influenced by local currents and
groundwater/seawater mixing. This has also been confirmed by a relatively short residence time of 1-2 weeks for water within 25 km
offshore, as obtained by short-lived radium isotopes. The irregular distribution of SGD seen at Ubatuba is a characteristic of fractured
rock aquifers, fed by coastal groundwater and recirculated seawater with small admixtures of groundwater, which is of potential
environmental concern and has implications on the management of freshwater resources in the region.

Here we present high-precision (2σ = ±3 ppm) 87Sr/86Sr measurements in coastal waters, together with salinity, to evaluate water mass mixing and the influence of submarine groundwater discharge (SGD) in coastal waters and ...

All Items in WHOAS are protected by original copyright, with all rights reserved, unless otherwise indicated. WHOAS also supports the use of the Creative Commons licenses for original content.
A service of the MBLWHOI Library |
About WHOAS